What you have there is a Puzzle and Dragons TypeX3 that was converted to USFIV. What kills the value of these is the cost of shipping, however if you can find a local buyer or someone within Norway. I'd say $250 ~ $300 wouldn't be a bad price.
They can, I've seen them die before.
If the PSU is working, then it would be very unlikely for it to be anything else. Regardless you'd need to open the PSU to find out. Just be careful as PSUs are dangerous.
1.) The video card is a 7900GT and not a 7900GS? It might not have the proper BIOS.
2.) Ensure your DVI to VGA adapter is a DVI-I to VGA and not a DVI-D to VGA
3.) Potentially a Vewlix L monitor setting?